1. Field of the Invention
The present invention relates to an inkjet recording apparatus having an inkjet recording head for discharging ink droplets, and an inkjet recording method using the inkjet recording head.
2. Description of the Related Art
Inkjet recording apparatuses having an inkjet recording head have been known as recording apparatuses capable of outputting high-quality characters and images at low cost. The inkjet recording head discussed in Japanese Patent No. 3343875 is provided with nozzles for discharging ink droplets. As a method for manufacturing the nozzle, a method of laminating a resin layer on a silicon substrate has been known.
FIG. 14 is a plan view illustrating nozzles provided in a known inkjet recording head. FIG. 15 is a cross-sectional view taken along the section line C-C illustrated in FIG. 14.
In a known inkjet recording head 101, a silicon substrate 100 and a resin layer 200 laminated on the silicon substrate 100 form a nozzle 300 (see FIG. 15). In the nozzle 300, ink filled in a pressure chamber 320 is heated by heat generated by an electrothermal converter 330. This causes film boiling and generates bubbles, and ink droplets of a predetermined amount are discharged from a discharge port 340. Then, the ink is refilled in the pressure chamber 320 from a supply port 110 passing through the silicon substrate 100 via a flow path 310.
In the inkjet recording head 101, a refill time (the time necessary for ink refilling) depends on the structure of the flow path 310. A flow path with a small sectional area requires longer refill time since the flow resistance in the flow path 310 is large. In such a case, a refill frequency (the number of times of the refill repeated in one nozzle per unit time) decreases. Consequently, a discharge frequency (the number of times of the discharge of ink droplets in one discharge port per unit time) also decreases. Therefore, high-speed recording is disturbed. On the other hand, if the refill time is too short (the flow resistance of the flow path 310 is very small), meniscus of the ink may overshoot and the ink may overflow from the discharge port 340. Consequently, to achieve stable high-speed recording, it is desirable to define an upper limit value and a lower limit value of the refill frequency and control the refill frequency to be within the range.
In manufacturing the inkjet recording head 101 using the method discussed in Japanese Patent No. 3343875, the size (for example, a height H of the flow path 310) of a part relating to the flow resistance may vary between production lots. Since the flow resistance affects the refill frequency, the refill frequency may vary too. If the range of variance in the refill frequency is within an allowable range in which a stable high-speed recording can be performed, there are no problems in particular.
Meanwhile, in recent years, demands for further increase in recording speed in the inkjet recording apparatuses have been growing. To respond to the demands, if the above-described discharge frequency is set to be high, the lower limit value of the refill frequency necessarily becomes high. In such a case, the allowable range of the refill frequency in which a stable high-speed recording can be performed becomes narrow. Consequently, the range of variance in the refill frequency exceeds the allowable range, and the possibility of occurrence of discharge failure may increase.